Origen

The first people to ride pillion on horses were not necessarily sharing their mount. In the 15th century a pillion was a light saddle, especially one used by women. Pillion is one of the earliest words to have entered English from Gaelic, coming from Scottish Gaelic pillean and Irish pillín ‘small cushion’, the root of which is Latin pellis ‘skin’, the source also of pelt (Middle English). The sense ‘seat behind a motorcyclist’ dates from the late 19th century

Origen

The first people to ride pillion on horses were not necessarily sharing their mount. In the 15th century a pillion was a light saddle, especially one used by women. Pillion is one of the earliest words to have entered English from Gaelic, coming from Scottish Gaelic pillean and Irish pillín ‘small cushion’, the root of which is Latin pellis ‘skin’, the source also of pelt (Middle English). The sense ‘seat behind a motorcyclist’ dates from the late 19th century